The invention relates to hydrotreating and aromatics saturation of lube oil stocks.
Low viscosity motor oils are desirable for better fuel economy. These oils must exhibit a high viscosity index in order to provide best results.
Highly paraffinic stocks have a high viscosity index but an unacceptably high pour point as well. It is necessary to remove the wax components from these stocks in order to provide an acceptably low pour point. Since the wax components contribute to a high viscosity index, their removal reduces the viscosity index of the product. Yield of product is reduced as well. The wax components are most commonly removed by solvent dewaxing. Techniques for obtaining both improvements in yield and in the viscosity index of a product having an acceptably low pour point are much sought after.
One such technique is catalytic dewaxing. In catalytic dewaxing, the high pour point waxy components are converted to lower pour point components, preferably lower pour point components which have a good viscosity index. However, the procedure causes some reduction in yield. Also, aromatic and heteroatom constituents, which are poor contributors to viscosity index, are not converted or removed by this technique.
Hydrotreating can be used for heteroatom removal. The technique is commonly referred to as hydrodesulfurization/hydrodenitrogenation, abbreviated as HDS/HDN. HDS/HDN removes sulfur and/or nitrogen containing species which are poor contributors to viscosity index. However, some loss in yield is experienced.
Aromatics saturation can be used to convert the aromatic species. The aromatic components do not contribute to viscosity index as greatly as do their saturated products and their saturation does not markedly decrease yield.
Several companies have developed technologies which effectively saturate aromatics in lube stocks but all of these processes employ very severe operating conditions including very high pressure (2000-3000 psi), temperature (up to 700.degree.+F.), low space velocities (0.25-1.0 LHSV), and high hydrogen consumption. The catalysts used are deactivated by sulfur and/or nitrogen in the feed. A process which effectively saturates aromatics in lube stocks at mild processing conditions and is capable of accommodating sulfur and nitrogen in the feed would be very desirable.